Add interface for a file loader rather than an importer
Change node to use the file loader interface
start seperating browser load stylesheet and loadFile
Move parsing into loadStylesheet from loadFile
move browser to parse inside parser
seperate sheet and env
Simplify more of loadFile and make more of the env creation common between node and browser
move new parseEnv into parser
Align the callback param orders
Add import inline option. Fixes #1209